Fluid motors

ABSTRACT

A fluid motor arrangement comprises a double-acting piston element which is slidably mounted in a cylinder element and the two axial sides of which have unequal effective areas, and a valve for controlling the admission of pressure fluid to the cylinder at opposite sides of the piston. The valve comprises a valve body member in which a spool valve member is slidably mounted. The valve body provides therein two chambers the pressures in which respectively act upon axially oppositely facing surfaces of the spool valve member, the ratio of the effective areas of said surfaces to each other being the same as that of the effective areas of the two sides of the piston. The (first) chamber having the larger of the two effective areas of the spool valve member is in permanently open communication with the cylinder at that side of the piston having the larger effective area, and the (second) chamber having the smaller of the two effective areas of the spool valve member is in permanently open communication with the cylinder at that side of the piston having the smaller effective area. The construction and arrangement is such that when the valve is operated in either sense from an initial position to actuate a movement of the fluid motor, the resulting variation in the pressures applied in said first and second chambers of the valve tends to return the valve to its initial position.

United States Patent Baxter 51 Sept. 19,1972

[ 1 FLUID MOTORS [72] Inventor: Michael David Baxter, Rochester,

England Primary ExaminerPaul L. Maslousky Attorney-Milton J. Wayne ABSTRACT A fluid motor arrangement comprises a double-acting I5 5 T l 58 5g 44 as so s z 64 60 5s piston element which is slidably mounted in a cylinder element and the two axial sides of which have unequal effective areas, and a valve for controlling the admission of pressure fluid to the cylinder at opposite sides of the piston. The valve comprises a valve body member in which a spool valve member is slidably mounted. The valve body provides therein two chambers the pressures in which respectively act upon axially oppositely facing surfaces of the spool valve member, the ratio of the effective areas of said surfaces to each other being the same as that of the effec tive areas of the two sides of the piston. The (first) chamber having the larger of the two effective areas of the spool valve member is in permanently open communication with the cylinder at that side of the piston having the larger effective area, and the (second) chamber having the smaller of the two effective areas of the spool valve member is in permanently open communication with the cylinder at that side of the piston having the smaller effective area. The construction and arrangement is such that when the valve is operated in either sense from an initial position to actuate a movement of the fluid motor, the resulting variation in the pressures applied in said first and second chambers of the valve tends to return the valve to its initial position.

6 Claims, 3 Drawing Figures FLUID MOTORS This invention relates to fluid motors and more particularly relates to fluid motor arrangements. The invention has a particularly useful but not exclusive application in power steering apparatus.

According to this invention there is provided a fluid motor arrangement comprising a double-acting piston element which is slidably mounted in a cylinder element and the two axial sides of which have unequal effective areas, and a valve for controlling the admission of pressure fluid to the cylinder at opposite sides of the piston, which valve comprises a valve body member and a spool valve member slidably mounted in the body member, the valve body providing therein two chambers the pressures in which respectively act upon axially oppositely facing surfaces of the spool valve member, the ratio of the effective areas of said surfaces to each other being the same as that of the effective areas of the two sides of the piston. the (first) chamber having the larger of said two effective areas of the spool valve member being in permanently open communication with the cylinder at that side of the piston having the larger effective area, and the (second) chamber having the smaller of said two effective areas of the spool valve member being in permanently open communication with the cylinder at that side of the piston having the smaller effective area, the construction and arrangement being such that when the valve is operated in either sense from an initial position to actuate a movement of the fluid motor, the resulting variation in the pressures applied in said first and second chambers of the valve tends to return the valve to its initial position.

Preferably the valve is secured to one of the elements of the fluid motor. Conveniently the line of action of the spool valve member is parallel or colinear with that of the fluid motor.

According to a preferred feature of the invention, the line of action of the spool valve member is colinear or substantially colinear with that of the fluid motor, and that element of the valve which is movable relative to the motor is actuated by a pin mounted on the fluid motor element which has the valve secured thereto, the pin being capable of a limited lost motion relative to the fluid motor element in the direction of said lines of action.

In one construction according to the invention, the fluid motor and the valve are accommodated end to end in a tubular housing, the valve body member being secured to the cylinder element of the fluid motor, the piston rod of the fluid motor projecting from the end of the cylinder remote from the valve, said first chamber communicating with the cylinder at the side of the piston adjacent the valve through a passage in the end wall of the cylinder, and said second chamber communicating with the cylinder at the side of the piston remote from the valve through an annular passage formed between the cylinder and said tubular housing and a part in the cylinder at or adjacent the end of the cylinder remote from the valve.

The invention also provides a fluid motor arrangement comprising a double-acting piston and cylinder motor whereof the two axial sides of the piston have unequal effective areas, and a valve operable to control a supply of pressure fluid to actuate the motor in either sense, which servo valve includes a cylinder and a plunger slidable in the cylinder, the cylinder and plunger together providing two chambers the pressures in which act upon oppositely facing surfaces of the plunger, the ratio of the effective areas of said surfaces of the plunger being the same as that of the said effective areas of the piston, the chamber having the larger effective area being in permanently open communication with the motor cylinder at the axial side of the piston having the larger effective area, and the chamber having the smaller effective area being in permanently open communication with the motor cylinder at the axial side of the piston having the smaller effective area, the construction and arrangement being such that when the valve is operated in either sense from an initial position to actuate a movement of the fluid motor, the resulting variation in the pressures in said first and second chambers of the valve tends to return the valve to its initial position.

One embodiment of the invention will now be described by way of example with reference to the accompanyin g drawings in which:

P16. 1 shows in axial section a fluid motor arrangement according to the invention,

FIG. 2 is a part-sectional plan of the fluid motor arrangement, and

FIG. 3 is an end view of the fluid motor arrangement in the direction of the arrow 3 of FIG. 1.

Referring to the drawings, the fluid motor arrangement shown is for connection between the pitman of the steering box of a motor vehicle and a fixed point on the chassis of the vehicle. The arrangement includes a double-acting fluid motor 10 and a valve 11, the latter and the cylinder 12 of motor 10 being accommodated in a tubular casing 13. Casing 13 has an end member 14 into which is screwed an end cap 15, and a distance sleeve 16 has one end spigoted on the end cap and in abutment with an axial shoulder 15a on the end cap and has its other end in similarly spigoted abutment with an axial shoulder 17a on an end piece 17 sealingly disposed in an internal rebate in one end of the valve body 18. The valve body 18 is a close fit in the tubular casing 13, and a sealing ring 19 in a groove at the end of the body prevents fluid from leaking past the body. The fluid motor cylinder 12 has an end member 20 which is in spigoted sealing engagement with the central bore 21 of the valve body and which abuts the valve body. An annular space 22 is formed between the cylinder 12 and the tubular casing 13.

At its end remote from the valve the cylinder 12 has an annular end member 23 which has sealing rings 23b, 23a to form seals respectively with the internal surface of the tubular casing and with the external surface of the piston rod 24 which is slidingly mounted in the end member. The adjacent end of the tubular casing is closed by an annular end cap 25 which is screwed into the tubular casing and which abuts the end member 23. End cap 25 incorporates a sealing ring 25a to form a seal with the piston rod.

The piston rod 24 has a piston 26 secured on its end by a nut 27, and the effective areas of the two faces of the piston are thus unequal. At its end remote from the piston, the piston rod carries a pair of rubber cushion elements 30 backed by washers 31 and held in position by a nut 32 on the end of the rod. When installed on a vehicle, the cushion elements are disposed on opposite sides of a fixed apertured bracket on the chassis of the vehicle and form a resilient spigot mounting for the piston rod and hence for one end of the complete fluid motor assembly.

The valve has a spool valve member 33 slidably mounted in its central bore 21, and one end portion 34 of the spool is reduced in diameter and projects through a central aperture in the end piece 17 and has pivotally connected to it one end of a short link 35. This link 35 has an aperture at its other end in which is secured a self aligning bearing 36 carrying a pitman stud 37. Stud 37 has a shoulder 38 against which is disposed a washer 39, and a first distance sleeve 40 encircling the stud extends between washer 39 and bearing 36. A second distance sleeve 41 encircles the stud at the other side of the bearing and this assembly is held together by a nut 42 on one end of the stud, the nut abutting sleeve 41 through a washer 43. The stud and its sleeves extend through slots 44, 45 which are formed in the end member 14 and distance sleeve 16 to permit the stud a measure of lost motion relative to the casing in a direction lengthwise of the casing, so that movement of the stud in this direction produces a corresponding movement of the valve spool 33. Cushioning washers 46 are disposed in the slots 44 between washers 39, 43 and washers 47 which cover the slots 44.

A first chamber 50 is formed between the valve body and the reduced diameter end portion 34 of the valve spool, and this chamber communicates, through an annular recess 52 in the end piece 17 and axial and radial passages 53, 54 in the valve body, with a passage 55 in the cylinder end member 20 leading to the cylinder space 56 at the front side of the piston.

The valve spool 33 has a central axial bore 58 which opens to the end face thereof adjacent the fluid motor, and a plunger 59 provided with a sealing ring 60 is freely slidably mounted in the counterbored outer end portion of bore 58, thus forming a second chamber 61. Plunger 59 is axially shorter than chamber 61 and in operation of the arrangement is held in abutment with the end member 20 of the motor cylinder by the pressure in chamber 61. A radial bore 62 in the spool extends from the central bore58 and opens to an annular recess 63 formed in the valve body and encircling the spool. From recess 63 a passage 64 leads through the body and opens to the annular space 22 between cylinder 12 and casing 13. This space communicates with the cylinder space 65 at the rearward side of the piston through apertures 66 in the cylinder.

The axial passage 53 communicates through a radial passage 70 with an annular chamber 71 formed by a groove in the spool. At its ends the camber 71 overlaps annular recess 63 and a similar annular recess 72 which is formed in the valve body and which encircles the spool. Pressure fluid is supplied into annular recess 63 from a pressure source through a union piece 74 (FIG. 2) which is screwed into the valve body and which has a supply pipe 75 connected to it. A second union piece (FIG. 3) screwed into the valve body places recess 72 permanently in communication with a reservoir for fluid exhausted from the motor and valve.

The arrangement illustrated is installed to extend transversely of a motor vehicle, the end of the piston rod being flexibly anchored to a fixed bracket on the chassis of the vehicle as previously described. Two lugs 76 on the tubular casing 13 have the ends of the steering track arms (not shown) pivotally connected to them respectively, and the pitman stud 37 has the end of the steering pitman arm secured to it by a nut (not shown). The pitman arm is arranged so that it swings about an axis which is in a fore-and-aft extending vertical plane of the vehicle, so that the swinging end of the pitman moves generally transversely of the vehicle. The resilient cushion elements 30 accommodate the resulting slight pivotal movement of the assembly about the fixed bracket.

When the piston 26 is stationary and spool 33 is in its central position, pressure fluid enters recess 63 from pipe and, and because chamber 71 overlaps recesses 63 and 72, flows into recess 72 and thence returns to the reservoir. Recess 63 is in permanently open communication with cylinder space 65 through passages 64, 22.

The pressure exerted in cylinder space 56 is less than that in space 65 because of the pressure drop across the small gap between recess 63 and chamber 71, but is of course applied to the side of the piston having the greater area.

A steering movement causes the pitman arm to swing and causes a corresponding movement of the pitman stud 37, and hence of the valve spool, relative to the tubular casing. The forces applied to the spool by the fluid pressures in the chambers 50 and 61 are insufficient to prevent this movement of the spool by the pitman arm. If this spool is moved in the direction of the arrow X indicated on link 35, the communication between recess 63 and chamber 71 is cut off. The pressure fluid therefore flows from recess 63 through passages 64, 22 to cylinder space 65, and causes the cylinder 12 and tubular casing 13 to move to the right, i.e., in the direction of arrow X, in which direction the pitman stud is being urged to move by the said steering movement. The fluid which is displaced from cylinder space 56 flows through passages 55, 54, 53 and 70 to chamber 71 and thence into recess 72 and to the reservoir, the overlap between chamber 71 and recess 72 having been increased by the movement of the spool in direction of the arrow X. When the extent of movement of the tubular casing is such as to bring the spool and body to their initial relative positions, the original conditions are restored and movement of the cylinder 12 relative to piston 26 ceases.

When the spool is moved by the pitman stud in the direction of the arrow Y, the communication between chamber 71 and recess 72 is cut off, and the pressure fluid is supplied to cylinder space 56 through chamber 71 and passages 70, 53, and 55. The pressure of the fluid is thus applied in both of the cylinder spaces 56 and 65 and is substantially the same in both spaces, and in consequence the cylinder 12, tubular casing 13 and the pitman stud together move in the direction of arrow Y owing to the greater efl'ective area of the piston bounding cylinder space 56. Fluid displaced from cylinder space 65 flows back to recess 63 and thence into cylinder space 56. By making the effective area of the rearward face of the piston half that of the front face, the response of the fluid motor to opposite movements of the spool can be made the same. As before, when the movement of the cylinder 12 is such as to bring the pitman stud and the spool back to their central positions as illustrated, movement of the cylinder ceases.

In the above explanation, the forces acting on the spool by reason of the pressures in chambers 50 and 61 have been largely ignored, but for correct equilibrium conditions, the forces on the spool must be balanced when the spool is in its central position. If the effective areas of the front and rear sides of the piston 26 are A and A, respectively, if the effective areas of the spool in chambers 50 and 61 are a, and a,, respectively, if P, is the pressure of the fluid applied to areas A and a,, and if P, is the pressure of the fluid applied to areas A, and

then for equilibrium of the piston P XA, =P XA and for equilibrium of the spool P, Xa, =P Xa.

therefore PJP, ri /A, =0 a,

i.e., the ratio of the effective areas of the spool in the chambers 50 and 61 must be the same as that of the effective areas of the front and rear faces of the piston.

When the spool is moved in the direction of arrow X, overcoming the forces on the spool, the pressure in cylinder space 56 and chamber 50 drops because the fluid from space 56, with which the chamber is in permanently open communication, is being driven into the reservoir, whilst the pressure in cylinder space 65 tends to rise because the incoming fluid is all directed into space 65 and because of the external resistance to movement of the cylinder 12. The pressure in chamber 61 therefore rises also, because this chamber is in permanently open communication with space 65. Thus a resultant force is produced on the spool tending to push the spool back into its central position. In a similar manner, movement of the spool in the direction Y produces a restoring force tending to return the spool to its central position. When movement of cylinder 12 ceases and the spool is returned to its central position, the spool is once again in stable equilibrium.

The invention also provides a fluid operated fluid motor arrangement including a piston and cylinder fluid motor and a plunger and cylinder valve, wherein the motor cylinder and the valve cylinder are connected together end-to-end, the plunger being adapted for connection to an operating member and the piston having a piston rod projecting from the motor cylinder at the end of the motor cylinder remote from the valve cylinder, the construction and arrangement being such that movement of the plunger towards or away from the motor cylinder produces a movement of the motor cylinder respectively towards or away from the projecting end of the piston rod.

Adjustment of the motor is accomplished by rotation of the two threaded end caps 15, 25. This causes the entire inner assembly constituted by the components 15, 45, 17, ll, 20, 12, 23, 25 to be adjusted axially relative to the outer assembly 13, 14 the pitman stud 46, link 35 and the valve member 33. This enables the initial setting of the motor valve assembly to be speedily, correctly adjusted at the test stage after assembly. If desired, a bias can be incorporated, for example to counter an excessive road camber.

lclaim:

1. A fluid motor arrangement comprising a doubleacting piston element which is slidably mounted in a cylinder element and which has two axial sides with unequal effective areas, and a valve for controlling the admission of pressure fluid to the cylinder element at opposite sides of the piston element, which valve comprises a valve body member and a spool valve member slidably mounted in the body member, the valve body member providing therein two chambers the pressures in which respectively act upon axially oppositely facing surfaces of the spool valve member, the ratio of the effective areas of said surfaces to each other being the same as that of the effective areas of the two sides of the piston element, the (first) chamber having the larger of said two effective areas of the spool valve member being in permanently open communication with the side of the piston element having the larger effective area, and the (second) chamber having the smaller of said two effective areas of the spool valve member being in permanently open communication with the side of the piston element having the smaller effective area; the axial side of the piston element having the smaller effective area being in permanently open communication with the source of fluid under pressure, and the spool valve member and the valve body member together providing a central groove and two flanking grooves which, in the initial position of the valve, are respectively in flow-restricting overlapping relationship with opposite ends of the central groove, the central groove being in communication with the larger effective diameter side of the piston element, and the two flanking grooves being respectively arranged for open communication with said source of fluid under pressure and a drain, relative sliding movement of the valve body member and spool valve member in opposite directions serving to reduce the overlap between the central groove and one of the flanking grooves and to increase the overlap between the central groove and the other flanking groove.

2. A fluid motor arrangement as claimed in claim 1, wherein the valve body member is fixed with respect to the cylinder element and the line of action of the spool valve member is colinear with that of the piston element, and wherein a stud is mounted on the valve body member for limited movement relative thereto in the direction of said line of action, said stud being connected to the spool valve member.

3. A fluid motor arrangement as claimed in claim 1 wherein the piston and cylinder elements and the valve are accommodated end to end in a tubular housing, the valve body member being secured to the cylindrical element of the fluid motor, the piston element of the fluid motor having a piston rod which projects from the end of the cylinder element remote from the valve, said first chamber communicating with the side of the piston element adjacent the valve through a passage in the end wall of the cylinder element, and said second chamber communicating with the cylinder element at the side of the piston element remote from the valve through an annular passage formed between the cylinder element andzsaid tubular housing and a part in the cylinder element at or adjacent the end of the cylinder element remote from the valve.

4. A fluid motor arrangement as claimed in claim 3, wherein the tubular housing has two external lugs at spaced positions along its length.

5. A fluid motor arrangement as claimed in claim 3, wherein threaded end caps are screwed into opposite ends of the tubular housing, and the ends of the valve body member and the cylindrical element remote from each other are in abutment with the two end caps respectively, whereby the relative axial position of the housing and the valve body member is adjustable.

6. A fluid motor arrangement comprising double-acting piston and cylinder elements whereof the piston element has two axial sides which have unequal effective areas, and a valve operable to control a supply of pressure fluid to actuate the piston element in opposite directions, which valve includes a valve body member and a spool valve member slidable in the valve body member in opposite directions from an initial central position; the axial side of the piston element having the smaller effective area being in permanently open communication with a source of fluid under pressure; the spool valve member and the valve body member together providing a central groove and two flanking grooves which, in the initial central position of the valve, are respectively in flow-restricting overlapping relationship with opposite ends of the central groove,

the central groove being in communication with the larger effective diameter side of the piston element, and the two flanking grooves being respectively arranged for open communication with said source of fluid under pressure and a drain, relative sliding movement of the valve body member and spool valve member in opposite directions serving to reduce the overlap between the central groove and one of the flanking grooves and to increase the overlap between the central groove and the other flanking groove; the valve body member and spool valve member together providing two chambers the pressures in which act upon oppositely facing surfaces of the spool valve member, the ratio of the effective areas of said surfaces of said spool valve member being the same as that of the said effective areas of the piston element, the chamber having the larger effective area being in permanently open communication with the axial side of the piston element having the larger effective area, and the chamber having the smaller effective area being in permanently open communication with the axial side of the piston element having the smaller effective area, the construction and arrangement being such that when the valve is operated in either sense from an initial position to actuate a movement of the motor, the resulting variation in the pressures in said first and second chambers of the valve tends to return the valve to its initial position. 

1. A fluid motor arrangement comprising a double-acting piston element which is slidably mounted in a cylinder element and which has two axial sides with unequal effective areas, and a valve for controlling the admission of pressure fluid to the cylinder element at opposite sides of the piston element, which valve comprises a valve body member and a spool valve member slidably mounted in the body member, the valve body member providing therein two chambers the pressures in which respectively act upon axially oppositely facing surfaces of the spool valve member, the ratio of the effective areas of said surfaces to each other being the same as that of the effective areas of the two sides of the piston element, the (first) chamber having the larger of said two effective areas of the spool valve member being in permanently open communication with the side of the piston element having the larger effective area, and the (second) chamber having the smaller of said two effective areas of the spool valve member being in permanently open communication with the side of the piston element having the smaller effective area; the axial side of the piston element haviNg the smaller effective area being in permanently open communication with the source of fluid under pressure, and the spool valve member and the valve body member together providing a central groove and two flanking grooves which, in the initial position of the valve, are respectively in flow-restricting overlapping relationship with opposite ends of the central groove, the central groove being in communication with the larger effective diameter side of the piston element, and the two flanking grooves being respectively arranged for open communication with said source of fluid under pressure and a drain, relative sliding movement of the valve body member and spool valve member in opposite directions serving to reduce the overlap between the central groove and one of the flanking grooves and to increase the overlap between the central groove and the other flanking groove.
 2. A fluid motor arrangement as claimed in claim 1, wherein the valve body member is fixed with respect to the cylinder element and the line of action of the spool valve member is colinear with that of the piston element, and wherein a stud is mounted on the valve body member for limited movement relative thereto in the direction of said line of action, said stud being connected to the spool valve member.
 3. A fluid motor arrangement as claimed in claim 1 wherein the piston and cylinder elements and the valve are accommodated end to end in a tubular housing, the valve body member being secured to the cylindrical element of the fluid motor, the piston element of the fluid motor having a piston rod which projects from the end of the cylinder element remote from the valve, said first chamber communicating with the side of the piston element adjacent the valve through a passage in the end wall of the cylinder element, and said second chamber communicating with the cylinder element at the side of the piston element remote from the valve through an annular passage formed between the cylinder element and said tubular housing and a part in the cylinder element at or adjacent the end of the cylinder element remote from the valve.
 4. A fluid motor arrangement as claimed in claim 3, wherein the tubular housing has two external lugs at spaced positions along its length.
 5. A fluid motor arrangement as claimed in claim 3, wherein threaded end caps are screwed into opposite ends of the tubular housing, and the ends of the valve body member and the cylindrical element remote from each other are in abutment with the two end caps respectively, whereby the relative axial position of the housing and the valve body member is adjustable.
 6. A fluid motor arrangement comprising double-acting piston and cylinder elements whereof the piston element has two axial sides which have unequal effective areas, and a valve operable to control a supply of pressure fluid to actuate the piston element in opposite directions, which valve includes a valve body member and a spool valve member slidable in the valve body member in opposite directions from an initial central position; the axial side of the piston element having the smaller effective area being in permanently open communication with a source of fluid under pressure; the spool valve member and the valve body member together providing a central groove and two flanking grooves which, in the initial central position of the valve, are respectively in flow-restricting overlapping relationship with opposite ends of the central groove, the central groove being in communication with the larger effective diameter side of the piston element, and the two flanking grooves being respectively arranged for open communication with said source of fluid under pressure and a drain, relative sliding movement of the valve body member and spool valve member in opposite directions serving to reduce the overlap between the central groove and one of the flanking grooves and to increase the overlap between the central groove and the other flanking groove; the valve body member and spool valve member together providing two chambers the pressures in which act upon oppositely facing surfaces of the spool valve member, the ratio of the effective areas of said surfaces of said spool valve member being the same as that of the said effective areas of the piston element, the chamber having the larger effective area being in permanently open communication with the axial side of the piston element having the larger effective area, and the chamber having the smaller effective area being in permanently open communication with the axial side of the piston element having the smaller effective area, the construction and arrangement being such that when the valve is operated in either sense from an initial position to actuate a movement of the motor, the resulting variation in the pressures in said first and second chambers of the valve tends to return the valve to its initial position. 